German Patent No. 33 28 875 discloses a dental technician's work station using a suction device which serves to remove dust caused by grinding or milling plastic, plaster or metal models with a hand grinder. The type of machining bit used in the typical rotary machine device held by the technician varies according to the material to be treated and the degree of precision of the particular working step, for example, coarse milling or fine grinding; and various machining bit types require different speeds. Experience has shown that the speed of the grinder and/or the suction device is very often incorrectly set by the user; calculating or estimating errors are usually responsible for inaccurate speed settings. A speed adjustment when the machining bit or work piece is changed is often not performed, not only on the hand grinder but also on the suction device, since speed adjustment on the known grinding or suction tools is often complicated and time consuming.
In dental technology, a wide range of machining bits is used, from disk millers or cutting disks with up to 50 mm diameter at one end of the scale to polishing heads with just a few millimeters diameter at the other end. Dependent on the cutting material used, for example hardened alloys or diamond, machining bit manufacturers recommend varying cutting speeds. If the speed is unduly high as a result of a faulty or omitted speed setting, there is the danger that machining bit portions such as cutting disks or diamond particles are split off due to the increased peripheral speed, thus endangering the dental technician. On the other hand, if the peripheral speed set is too low, the surface finish and cutting performance of the grinder are adversely affected.
The suction device is also adversely affected if the speed of the suction fan is too high or low. If too high, than excessive noise occurs at the work station, as well as high energy consumption; a low speed not matching the particular work stage results in insufficient suction by the suction fan, hence the dust from grinding is inhaled by the dental technician or may settle in the surroundings.